1. Field of the Invention
The present invention relates to a gas sensor element and a ceramic heater to heat the gas sensor element.
2. Description of the Related Art
A gas sensor is provided in an exhaust gas system of a vehicle internal combustion engine. The gas sensor detects a concentration of a specific gas contained in a gas to be measured such as an exhaust gas. The gas sensor has a built-in ceramic heater for heating a gas sensor element.
For example, there is a ceramic heater having a heater pattern formed on a surface of a ceramic substrate. The heater pattern has a heating element that generates heat when a current is passed therethrough and a lead portion that conducts electricity to the heating element.
Recently, there is a tendency to reduce the specific resistance of heating elements, since gas sensor elements are required, for example, to warm up rapidly (early-activation) and to be used, under high temperature.
For example, JP-A-2004-342622 discloses a ceramic heater. The ceramic heater is configured such that the heating element and the lead portion are made of a different material, and that the heating element has lower specific resistance than the lead portion. In this ceramic heater, since the heating element, and the lead portion, are made of a different material, the end of the heating element and the end of the lead portion are overlaid with each other, for example, thereby joining the heating element and the lead portion.